Intraocular pressure recording system

ABSTRACT

A new noninvasive approach for intraocular pressure (IOP) measurement allowing continuous monitoring over prolonged periods, regardless of patient&#39;s position and activities. The key element of this measurement method is a soft contact lens ( 1 ) including at least one strain gage ( 2 ) longitudinally arranged around the center of the contact lens and capable of measuring precisely spherical deformations of the eyeball induced by the changes in IOP. This information is transmitted with wires or (preferably) wirelessly in real time to an external recording system ( 14 ). The system is placed in the same way as a normal corrective contact lens, no anesthesia is required and patient vision remains almost completely unimpaired.

This application is the U.S. national phase of international applicationPCT/CH01/00407 filed 29 Jun. 2001 which designated the U.S., the entirecontent of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a device for recording the intraocularpressure over a period of time. More precisely, the invention relates toa device which can be placed on a contact lens on an eye to continuouslymonitor and record intraocular pressure over an extended period of time,e.g. 24 hours or more.

STATE OF THE ART

Glaucoma is a widespread disease (2–4% of a given population)characterized by an elevated intraocular pressure (IOP). This elevatedIOP produces a gradual loss of peripheral vision.

There is therefore a need to have a detailed knowledge of IOP inglaucoma patients in order to provide reliable diagnostics or forsetting up new therapies.

U.S. Pat. No. 5,179,953 discloses an intraocular pressure recordingsystem made of scleral contact lens comprising a pressure transducerincluding one semiconductor strain gage which indents the sclera in afixed position. This results in a fixed indentation connection of thegage to the sclera.

U.S. Pat. No. 4,089,329 discloses an intraocular pressure recordingsystem made of a support, e.g. a ring, comprising a planar-facedpressure transducer which is adapted to crush (flatten) a portion of thescleral surface.

U.S. Pat. No. 4,922,913 discloses an intraocular pressure recordingsystem made of a semi-rigid contact lens which contains a pressuretransducer, e.g. a piezo-electric strain gage, which has a planarsurface flattening a central portion of the cornea.

The publication entitled “Intraocular pressure measurement withinstrumented contact lenses, Investigative Ophthalmology”, April 1974,pp. 299–302, Vol. 13, No 4. discloses an intraocular pressure recordingsystem made of a contact lens on which a strain gage is placed in ameridional angle of the corneosciera junction to measure angularchanges. This pressure measurement relies on the theoretically predictedcorrelation between IOP and angular changes.

The publication entitled “A scieral buckle pressure gauge for continuousmonitoring of intraocular pressure”, Myron et al., InternationalOphthalmology 2, 3: 11–17 (19890), discloses an implantable variableresistance pressure gage made of a strip which has to be placed andattached around the periphery of the sclera by a surgeon.

The publication entitled “Distensibility measurements of the rabbiteye”, Tittel & Richards, Investigative Ophthalmology, 1971, vol. 10, No10, 800–809, discloses the use of a circumference gage of the same typeof the scleral buckle pressure gauge which was implanted on rabbits.

The currently used devices are either too aggressive for the patient ornot accurate enough or do necessitate to topically anesthetize thepatient's eye and/or to surgically operate prior to testing.

Thus there is presently a need for a comfortable and accurate testingwhich simultaneously does not require a physician.

The present invention is directed to meeting the above cited needs. Itconcerns an intraocular pressure recording system comprising a softcontact lens and an active strain gage fixed to said contact lens,characterized by the fact that said active strain gage has a circulararc shape and is situated around the center of said soft contact lens.This particular configuration allows one to measure very preciselyspherical deformations of the eyeball which are correlated to IOP.

Using the object of the present invention allows a more accuratemeasurement of the eyeball and i.e. the IOP. Furthermore, due to thefact that the strain gage is not in direct contact with the eye, thepatient feels very comfortable and his vision remains almost completelyunimpaired. In fact he has a similar feeling as a person wearing usualcontact lenses.

In a preferred embodiment, the active strain gage is made of a resistivemetal, the gage resistance varying according to the gage strain.

Preferably the active strain gage is a continuous longitudinal element,e.g. a wire or a microfabricated object (MEMS) which result in a foilstrain gage on which a metallic layer is deposited or laminated on asubstrate (e.g. polyimide) and patterned by wet or dry etch in a desiredconfiguration (grid).

The wire diameter may be comprised between 0.01 mm and 0.1 mm.

MEMS gages are manufactured according to Integrated Circuitmanufacturing processes, this technique offers the following advantages:Every single parameter of the strain gage can be controlled veryprecisely (e.g. thickness of the metallic strain gage layer) as well asthe design of the grid that can be realized with a precision of about 1μm and gives the possibility to build really specific gages. Moreoverthe process is completely and easily reproducible.

As material which can be used for the gages of the present invention wecan cite Polyimide as substrate and platinum as metallic layer, but anykind of resistive material as well as semiconductor or resistive polymercould be used. Polyimide as substrate is really suitable because it iswell known and used in MEMS technology and it is biocompatible as wellas platinum which has also a good strain gage factor.

For a variable resistance pressure gage, in order to have a moreaccurate measurement, the gage resistance has to be maximized and itsgrid area has to cover all the zones which have to be monitored. In thepresent invention, this can be achieved by folding the longitudinalelement into several portions which are arranged parallel to each other.

In one preferred embodiment the active gage forms almost a completecircle.

Several active gages can be placed on the contact lens. They can consistof several circular arc portions placed along the same circumference orthey consist of several concentric circles.

In another embodiment, the intraocular pressure recording systemfurthermore comprises passive strain gages for thermal compensationwhich have preferably a general circular arc shape made of a continuousmeridional element placed in such a way that several of its portions areradially arranged, i.e. their direction cross the lens center C. Such aconfiguration results in a more accurate measurement.

In another preferred embodiment, the intraocular pressure recordingsystem comprise four gages in a Wheatstone Bridge configuration, e.g.two active gages and two passives ones being placed alternatively on thebridge.

The active gage(s) can be placed at any distance from the center of thecontact lens. In a preferred embodiment, the active gage is shaped inorder to be placed on the corneoscleral junction which represents a zonewhere changes in IOP induce maximum corneal deformation.

The gage(s) can be fixed to the lens by any method. It/They can be firstfixed to a substrate which is then fixed on the lens or it/they can bedirectly fixed to the lens.

The data transmission with the gage(s) can be achieved in using a wiretransmission or (preferably) a wireless transmission system.

In addition to the gage(s) the contact lens can also comprise othermeasuring devices such as an ElectroRetinoGraph or a chemical analysissensor.

The present invention will be more fully appreciated from the followingdetailed examples taken together with the drawings in which:

FIG. 1 shows a first intraocular pressure recording system according tothe invention.

FIG. 2 shows a second intraocular pressure recording system according tothe invention.

FIG. 3 shows a third intraocular pressure recording system according tothe invention.

FIG. 4 shows a strain gage which can be used with the present invention.

FIG. 5 shows another strain gage which can be used with the presentinvention.

FIG. 6 shows a simplified block diagram of an intraocular pressurerecording system according to the invention with a telemetry systemembedded and extracorporal receiving units.

As shown in FIG. 1 to 3, the intraocular pressure recording systemcomprises a soft contact lens 1 including a circular active strain gage2 disposed around the lens center C. Active strain gage 2 is made of acontinuous longitudinal wire which is folded in such a way that severalof its portions 3 are parallel to each other and therefore concentric.Both ends 4 of the wire are connected to a data transmission system (notillustrated). The transmission may be achieved via a wireless telemetrysystem.

FIGS. 2 and 3 illustrate another preferred device similar to the one ofFIG. 1 but comprising four gages in a Wheatstone Bridge configuration,e.g. two active gages and two passive ones being placed alternatively onthe bridge. The passive strain gages 5 are made of a continuous wirefolded into several portions 7 which are radially arranged, i.e. theirdirection cross the lens center C. The wire portions of active andpassive gages can be very close to minimize the gage area or more spacedto maximize thermal exchanges and gage area. FIG. 3 shows aconfiguration with a quite big passive gage area with wire portionsgrouped into more blocks 6. With such configurations (FIGS. 2 and 3),the two active strain gages 2 measure one type of strain (the strongestone) and double the sensitivity of the measure on the Wheatstone Bridge.The two passive strain gages 5 measure another type of strain (theweakest one) and compensate for thermal derivation, active and passivegages having the same resistance value without any stress applied.

FIG. 4 illustrates a strain gage 8 which is made of a wire 10 and FIG. 5illustrates another strain gage 9 (MEMS) with its grid 11 which is madeaccording to a micromachining process.

FIG. 6 shows the simplified block diagram of a preferred configurationof the entire system with a telemetry system embedded and extracorporalreceiving units. The contact lens comprise the sensor, it is to sayactive 2 and passive 5 gages on a Wheatstone Bridge configuration, alow-power transponder 12 and a loop antenna 13. Powering andcommunication are performed contactlessly between the transponder and anextracorporal mobile interrogation unit (MIU) 14 via coupled loopantennas. The MIU provides the sensor with energy and passes thereceived transponder data to the stationary data receiver (SDR) 15 via asecond RF link. The SDR completes the monitoring setup. It stores anddisplays the received data.

1. Intraocular pressure recording system comprising a soft contact lenshaving a center and an active strain gage fixed to said contact lens,wherein said active strain gage is placed at a distance from the centerof the contact lens, is not in direct contact with an eye, and comprisesa portion having a circular arc shape which is situated around thecenter of said soft contact lens.
 2. Intraocular pressure recordingsystem according to claim 1 wherein said active strain gage is made of aresistive material.
 3. Intraocular pressure recording system accordingto claim 2 wherein said active strain gage is a continuous longitudinalelement.
 4. Intraocular pressure recording system according to claim 3wherein said continuous longitudinal element comprises portions and isplaced in such a way that several of said portions are disposed parallelto each other.
 5. Intraocular pressure recording system according toclaim 3 wherein said continuous longitudinal element is microfabricated.6. Intraocular pressure recording system according to claim 3 whereinsaid continuous longitudinal element is a wire.
 7. Intraocular pressurerecording system according to claim 1 further comprising a passivestrain gage.
 8. Intraocular pressure recording system according to claim7 wherein said passive strain gage has a general circular arc shape madeof a continuous meridional element comprising portions and is placed insuch a way that several of said portions are radially arranged. 9.Intraocular pressure recording system according to claim 8 wherein saidcontinuous meridional element is microfabricated.
 10. Intraocularpressure recording system according to claim 8 wherein said continuousmeridional element is a wire.
 11. Intraocular pressure recording systemaccording to claim 7 including a wireless telemetry system for datatransmission with said passive strain gage.
 12. Intraocular pressurerecording system according to claim 7 including a wireless telemetrysystem for data transmission with said active and passive strain gages.13. Intraocular pressure recording system according to claim 1 whereinsaid active strain gage is shaped in order to be placed on thecomeosclera junction.
 14. Intraocular pressure recording systemaccording to claim 1 including a wireless telemetry system for datatransmission with said active strain gage.
 15. Intraocular pressurerecording system according to claim 1 wherein said contact lens furthercomprises other measuring devices.
 16. Intraocular pressure recordingsystem according to claim 1 wherein the system comprises several activegages.
 17. Intraocular pressure recording system according to claim 1wherein the system comprises several passive gages.
 18. Intraocularpressure recording system according to claim 1 wherein the systemcomprises gages in a Wheatstone bridge configuration.
 19. Intraocularpressure recording system according to claim 18 wherein the Wheatstonebridge configuration comprises two active gages and two passive gagesplaced alternatively on the bridge.
 20. Intraocular pressure recordingsystem according to claim 1 wherein said contact lens further comprisesan ElectroRetinoGraph or a chemical analysis sensor.
 21. Intraocularpressure recording system according to claim 1 wherein said contact lensis a silicone contact lens.
 22. Intraocular pressure recording systemcomprising: a soft contact lens having a center, an active strain gagefixed to said contact lens, wherein said active strain gage is placed ata distance from the center of the contact lens, is not in direct contactwith an eye, and comprises a portion having a circular arc shape whichis situated around the center of said soft contact lens, and a passivestrain gage, wherein said passive strain gage has a general circular arcshape made of a continuous meridional element comprising portions and isplaced in such a way that several of said portions are radiallyarranged.
 23. Intraocular pressure recording system comprising: a softcontact lens having a center, and an active strain gage fixed to saidcontact lens, wherein said active strain gage is placed at a distancefrom the center of the contact lens, is not in direct contact with aneye, and comprises a portion having a circular arc shape which issituated around the center of said soft contact lens, and wherein thesystem comprises gages in a Wheatstone bridge configuration.